1. Field of the Invention
The present invention relates generally to the fields of semiconductor manufacturing and deposition chambers. More specifically, the present invention relates to a method of improving the planarity of a susceptor during a deposition process.
2. Description of the Related Art
The fabrication of thin films as insulators, conductors, dielectrics or other layers upon a substrate, e.g., a semiconductor wafer or a glass plate, is accomplished by various deposition processes. Common among these are chemical vapor deposition (CVD) and physical vapor deposition (PVD or sputtering) processes both of which encompasses more specialized means of deposition. The application of such processes to a substrate requires that the substrate be disposed in a deposition chamber in such a manner that the resulting deposited thin film has optimal qualities, such as, inter alia, conformality, deposition rate uniformity across the substrate, thickness uniformity, and film smoothness, for its intended use.
To process substrates using these deposition techniques, a vacuum chamber may be provided having a susceptor configured to receive a substrate. A susceptor is a mechanical part that holds a substrate in a processing chamber for a fabrication step, e.g., CVD. For example, a CVD apparatus includes a susceptor positioned within a deposition chamber. The support plate of the susceptor supports a substrate, such as a glass panel or a semiconductor wafer, onto which a film of material is deposited by thermal decomposition of at least one precursor gas.
During a deposition process, the pressure is lowered to reduce the overall pressure in the deposition chamber. This results in forces pushing up on the undersurface of the susceptor because the susceptor shaft, usually a tube-like structure, is at atmospheric pressure. This pressure differential may cause the susceptor surface to deform or to “bow”. As substrate size increases with a necessary concomitant increase in susceptor size, this deformation is amplified. This causes the irregular deposition of thin films onto a substrate held on the susceptor surface.
Additionally, the materials usually used to manufacture susceptors are aluminum-based materials such a s aluminum nitride. Although resistive to process gases and contamination, susceptors manufactured from these materials significantly tend to lose rigidity at temperatures of about 300° C. or higher. The substrate support surface is, therefore, less likely to remain planar, particularly coupled with the pressure differential exerting force on the underside of the support surface.
In FIG. 1 deformation of an aluminum-based substrate 235 in a reduced pressure environment provided by a processing chamber 200 at temperatures at about 300° C. is depicted. As the pressure of the internal environment of the chamber 200 is drawn down below atmsopheric pressure by vacuum pumping 220 and as the temperature reaches about 300° C. or above, the reduced rigidity of the aluminum-based support plate 210 is acted upon by the unequal pressures on the top and underside of the support plate 210 and thereby deforms.
The susceptor shaft, being hollow and exposed to atmospheric pressure of about 760 Torr, also, therefore, exposes the undersurface of the center portion of the support plate 210 to atmospheric pressure. This may cause bowing 212 in the center portion of the upper face or support surface 216 of the susceptor plate 210, since the upper surface is exposed to the reduced pressure environment. At the same time, the edges of periphery of the susceptor plate 216 may sag 214 due to the reduced rigidity of the susceptor material and this may be exacerbated when bowing is present. Overall, the result is a nonplanar susceptor surface 216.
In a deposition process, the processing material to be deposited on the substrate must travel in some form from the input across the deposition chamber to the surface of the substrate. This distance, whether it is the input distance from a gas distribution plate to the substrate in a CVD application or the distance from a sputterable target to the substrate in a PVD application, can affect the deposition rate of the film onto the substrate. If the substrate is supported on a deformed susceptor plate as described above, the periphery of the substrate surface is at a greater distance from the input of the processing materials than is the center of the substrate surface. Thus the deposition rate at the center of the substrate surface is greater than at the periphery of the substrate surface. The resulting unevenly deposited film may be defective or incapable of performing a s intended.
Typically, a broader range of deposition processes can be conducted at higher temperatures. A greater variety of layers can be deposited at temperatures above about 300° C. It would be advantageous to provide an aluminum-based susceptor system that maintains a planar substrate support surface at temperatures of greater than about 300° C. and in a reduced pressure atmosphere.
Therefore, the prior art is deficient in the lack of effective means of improving the planarity of a susceptor during a deposition process. Specifically, the prior art is deficient in the lack of effective means of vacuum pumping on a susceptor shaft to improve the planarity of the susceptor surface. The present invention fulfills these long-standing needs and desires in the art.